Alcohol measuring devices are used especially in the combination with a vehicle immobilizer of a vehicle, a so-called “interlock system.” An interlock system comprises essentially two components: the alcohol measuring device, which is located in the interior space of the vehicle, as well as a control device, which is installed, as a rule, under the dashboard and establishes or blocks the power supply to a starting relay of the vehicle. After the vehicle ignition has been turned on, the interlock system asks the operator to provide a breath sample. The measurement result for the alcohol concentrations decides whether the starter of the vehicle is released and the engine can thus be started. Manipulation is possible, in principle, during the use of the interlock system based on an alcohol measurement by a second person, who is not the driver. To rule out such a possibility of circumvention, an interlock system usually has an alcohol measurement repeat function. Such a repeated measurement is required from the driver, for example, after a time interval generated according to the random principle. Yet, there is a possibility of multiple alcohol measurements by a second person who is not steering the vehicle.
An interlock system, which comprises a video camera, which selectively stores pictures, with a position sensor, which ensures that the video camera correctly detects the tester, is known from EP 1 591 296 A1. The video image is stored and can be sent to an analysis center for identification. The drawback of this device is, however, that identification of the tester takes place with a time delay or a comparison with a picture of the tester imposes high requirements on image processing.